1. Field of the Invention
The present invention relates to a bundle of permselective hollow fibers and a fluid separator containing the same. More particularly, the present invention is concerned with a bundle comprising a plurality of porous hollow fibers extending substantially in parallel and a plurality of filaments which intermingle with the hollow fibers substantially lengthwise over the length of the hollow fibers, and wherein substantially all of the filaments each engage with at least one of the hollow fibers, thereby placing the hollow fibers into an inseparable bundle. Further, the present invention is concerned with a fluid separator containing the bundle for use in the separation of a component or components from a liquid or a mixed gas, for example, for use in dialysis, ultrafiltration, osmosis, reverse osmosis, pressure separation of gas mixtures and the like.
The bundle of the present invention has not only a high packing ratio of hollow fibers, but also an effective arrangement for ensuring narrow but uniform spacings between hollow fibers and hence for efficiently exerting a high performance of each hollow fiber.
2. Discussion of Related Art
With respect to the fluid separator comprising hollow fibers, the demand for an apparatus having a small fineness but exhibiting a high performance is very strong in the art. To meet the strong demand, various proposals have been made.
U.S. Pat. No. 4,293,418 discloses a fluid separator comprising a bundle of a plurality of hollow fiber elements. Each of the hollow fiber elements consists of one or two permselective hollow fibers and a spacer yarn composed of a textured yarn. The spacer yarn is spirally wound around one or two hollow fibers, and the apparent thickness of the spacer yarn is 0.5 to 3 times the outer diameter of the hollow fiber, which outer diameter is 50 to 600 microns. The windings are regular, and the number of windings of the spacer yarn around each hollow fiber is 0.5 to 20 per 10 mm length of the hollow fiber. The hollow fiber packing ratio in the separator is 30 to 78%. When it is intended to obtain a hollow fiber packing ratio as high as 60% or above, the bundle of hollow fibers must be squeezed so as to have a decreased diameter prior to the incorporation into a tubular casing of a fluid separator. This squeezing is likely to be accompanied by a break of hollow fibers and hence by a poor assembly yield. The use of a spacer yarn having a small diameter which is selected in order to obtain a high hollow fiber packing ratio, causes the winding of the spacer yarn around the hollow fiber to be extremely difficult, and hence causes the mass production of the hollow fiber bundle to be infeasible. Moreover, since the spirally wound spacer yarn provides a spacing between the hollow fibers only at intervals and not continuously over the lengths of the hollow fibers, the function of the spacer yarn as a spacer is not satisfactory when the diameter of the spacer yarn is small. This causes poor separation efficiency. Therefore, according to the proposal of U.S. Pat. No. 4,293,418, it is difficult to attain both a high hollow fiber packing ratio and a high separation efficiency.
Japanese Patent Application laid-Open Specification No. 2-60658/1990 discloses a bundle of hollow fibers, a part of which are replaced by thick threads having no separating activity. From the proposal of the above-mentioned patent application as well, a bundle having both a high hollow fiber packing ratio and a high separation efficiency cannot be expected. Further, the employed thread has various modifications. For example, it may be longitudinally waved, or its diameter may be longitudinally changed. Further, it may be spirally wound. Still further, its surface may be uneven. The manufacturing of such a thread is difficult and costly.
U.S. Pat. No. 4,950,391 discloses a hollow fiber dialyzer comprising (1) a housing, (2) embedding compositions in the housing defining a dialyzing chamber between the compositions and defining blood inflow and outflow chambers outside the compositions between the compositions and the housing, (3) hollow fibers that are fastened at both ends and sealed to the embedding compositions so that the interiors of the fibers communicate with the inflow and outflow chambers, and that the exteriors of the fibers are exposed in the dialyzing chamber, and (4) spacing threads that are fastened at both ends in the embedding compositions, that are parallel to each other and the fibers, that are uniformly distributed in the dialyzing chamber and that are independent of the individual hollow fibers. The number of threads relative to the number of hollow fibers can be varied and modified to produce dialyzers of different capacity grades in spite of the use of one and the same housing. The threads serve to fill up dead (or unnecessary) spacings in the dialyzate chamber. The thread has approximately the same diameter or a diameter somewhat smaller than that of the hollow fiber. Depending on the capacity grade, one thread may be provided for about 10 to 25 hollow fibers, although the ratio of threads to hollow fibers may be varied. By the proposal of U.S. Pat. No. 4,950,391, a fluid separator having a small fineness but exhibiting a high separation efficiency cannot be obtained.